Radiographic imaging is often imperative for the pre-operative planning of surgical treatments for patients. Plain X-rays, computed tomography (hereinafter “CT”) images, and magnetic resonance (hereinafter “MR”) images facilitate surgical navigations. Because of their usefulness, surgeons have sought innovative ways to further incorporate radiographic imaging into the surgical suite. For years, orthopedic and vascular surgeons have relied upon intra-operative, real-time fluoroscopy, such as plain X-rays, to assess surgical treatments. More recently, real-time MR [1] and CT [2] imaging surgical suites have been constructed where intra-operative MR or CT image is continuously updated displaying anatomic changes due to surgical treatment. These systems have found limited use due to logistic difficulties including the exorbitant cost of a dedicated CT or MR imaging system in an operative suite and the physically confined environment in which a surgeon operates.
A more feasible option has been the use of pre-operative CT and/or MR images in an image-guided surgery (hereinafter “IGS”) where anatomic locations are continuously updated on the pre-operative CT and/or MR images as specified by a surgical probe. The concept of the image-guided surgery dated back to the 1940's [3]. However, widespread acceptance of the concept did not occur until radiographic advances in the 1970's that made CT and MR images routinely available. Image-guided surgical systems, which are analogous to global-positioning systems (hereinafter “GPS”), have since found widespread use in neurosurgery [4] and sinus surgery [5]. In general, An IGS system includes a pre-operative radiographic image (CT or MR image) that is acquired from a patient and digitized and stored on a computer. Within the operating room (hereinafter “OR”), the pre-operative radiographic image are registered to the anesthetized patient by correlating landmarks found on the pre-operative radiographic image with the landmarks on the anesthetized patient. Typical landmarks used for registration are anatomic points and/or fiducial markers attached to the skin or implanted in bone of a patient. Registration creates a transformation matrix that allows a direct mapping of the patient's current anatomy to the corresponding pre-operative radiographic image. Once registration has taken place, for example, using an electronically visible probe, such as infrared optical system and/or electromagnetic system, to detect a location of each fiducial marker in the patient, i.e., the physical space, that is registered to in a radiographic image space. The probe can be used as a pointer to identify surgical anatomy on CT or MR images.
Crucial to limiting error in IGS systems is registration of the pre-operative radiographic image to the surgical field of interest in the anesthetized patient. Registration landmarks, for example, anatomic landmarks and/or fiducial markers, need to be immobile relative to the anatomy and arranged such that they surround the surgical field of interest. While multiple anatomic landmarks would initially appear useful, soft tissue, for instance, skin and muscle, relaxes and distorts under general anesthesia making boney landmarks necessary for accurate registration. A solution has been to implant markers into bone of a patient. This is routinely used in neurosurgery where screws are placed into the cranium prior to pre-operative radiographic imaging and these screws serve as landmarks for registration. While accuracy with such systems is impressive [6, 7], it does involve the invasive placement of bone screws with small, yet real, risk of infection and cosmetic deformity. Another solution is to use skin markers or skin contours. Such systems have shown decreased accuracy that is unacceptable in otologic applications [8].
The most common ear disorders of human being that require surgical treatments are chronic serous otitis media (hereinafter “CSOM”) and cholesteatoma. The CSOM is characterized by inflammation of the mucous membrane lining the middle ear that does not respond to medical therapy. The cholesteatoma contains keratinizing squamous epithelium (skin) trapped within the middle ear cavity and leads to chronic infection, hearing loss, facial nerve paralysis, and vertigo. Both the CSOM and cholesteatoma are usually treated by an otologic surgery, for example, through a mastoidectomy, to remove diseased tissues from the temporal bone encasing the ear using a surgical drill and/or knife. As a result, adjacent structures surrounding the surgical site of the temporal bone, such as the facial nerve, the inner ear, the floor of the cranial vault, the internal jugular vein and the carotid artery, are at great risk during the surgical treatment.
It has been shown that IGS systems can improve overall standards of surgical treatments in both neurosurgery and sinus surgery. Specifically, IGS systems have improved surgical accuracy and reduce the risk of major complications in sinus surgery [9], and decreased operative time for neurosurgical procedures thus cutting costs [10]. In addition, patients treated with an IGS have more complete resection of diseased tissues with less collateral damage to healthy tissues [11] than that treated with a traditional surgery. It is anticipated that such advantages of the IGS systems would be also applicable to an otologic surgery. Epidemiologic and economic data supports the usefulness of an IGS in otologic procedures. However, applications have been limited by the need for millimeter and sub-millimeter accuracies to prevent injury to adjacent structures, such as the facial nerve and the inner ear.
Therefore, a heretofore unaddressed need still exists in the art to address the aforementioned deficiencies and inadequacies.